1. Field of the Invention
The present invention relates to hot melt inks for ink jet printers and, more particularly, to a hot melt ink that is solid at normal temperatures and used for printing after being thermally melted at temperatures higher than normal temperatures.
2. Description of Related Art
Ink jet printers have many advantages in printing techniques, such as noiselessness, high speed, high quality and coloration. However, ink droplets jetted from an ink jet nozzle are directly deposited onto recording paper, causing the print quality and print drying time to be influenced depending on the type of recording paper. If low-quality paper is used for recording, a considerable deterioration in quality of the resultant print has been experienced.
It is known that to solve this problem, hot melt ink having a melting point higher than room temperature is used, achieving print of a uniform dot size irrespective of the type of recording paper. Ink compositions for this purpose have been proposed including ink containing natural wax as disclosed in U.S. Pat. No. 4,390,369, ink containing stearic acid as disclosed in European Unexamined Patent Publication No. 99,682, and ink containing a C.sub.20 -C.sub.24 acid or alcohol along with a ketone having a relatively high melting point, in which all the inks make use of dyes as a coloring material. Moreover, in U.S. Pat. Nos. 4,659,383 and 4,822,418 hot melt inks are proposed in which solid pigments are dispersed in waxes or C.sub.18 -C.sub.24 fatty acids having a melting point higher than 65.degree. C.
However, the known hot melt inks for ink jet printers described above have problems such as the degree of dye solubility when dyes are used as the coloring material. This limits the types of dyes that can be used. In addition, the ink cannot necessarily be kept stabilized when heated over a long time or on repetition of heating and cooling cycles. Poor color fastness to light is another problem. On the other hand, when pigments are used as the coloring material, good color fastness to light is attained but the dispersability of the pigments and the stability of the dispersed pigments are not always satisfactory. As a result, the ink's storage stability under heating conditions is not good.